Piston cooling in free-piston units



Aug. 12, 1947.

W. A. LEDWITH PISTON COOLING IN FREE PISTON UNITS Filed March 27, 1945 4 Sheets-Sheet 1 W W R m U OM N 0 M m E m T N on b om V L T J Q mm A l JMF I 4 0 Q 0 mm 4 0 0 0 0 0 0 0 O o. 0 O O 0 0 o o mm o m mm m. v 00 mm m. o m m o E 0 0 QN 0 (C C rk f U Q Q Q Q 0 O O Q 3 w 0 0 O Q Q 4 Q 0 0 0 o H! 0 u. d9 m w w 34 N4 3 w o 3 Aug. 12, 1947. w, A V| YEDW|TH 2,425,544-

PIS'I'ON COOLING IN FREE PISTON UNITS V Filed March 27, 1945 4--SheetsSheet 2 WALTER A. LEDWITH ATTORNEY W. A. LEDWITH PISTON COOLING IN FREE.P.ISTON UfiITS 1945 4 Sheets-Sheet 5 Filed March 27 INVENTORQ ATTORNEY WALTER A. LEDWITH Aug. 12, 1947.

I1onII!III1|!aInI!!!vlllillllill!!!olallivuvonrllalllrln ll FIIIIIII! I11 1701441415417! 4 Aug. 12,1947.

W. A! .LEDWITH PISTON COOLING IN FREE PISTON UNITS 4 Sheets-Sheet 4 Filed March 27, 1945 Q O h A) JW O o 2. mm Q H 0 i 3 no o o Q on h a 06 P mm 3 .3 m m k r\ C [000 mm 9 Q AU 8 oh OQQ Q O \Y/ H O O 3 w. 3 .0 v N E. mm mm mm -v INVENTOR WALTER A. LEDWITH ATTORNEY Patented Aug. 12, 1947 PISTON COOLING IN FREE-PISTON- UNITS Walter A. Ledwith, Hartford, Conn, assignor to. United Aircraft Corporation, East Hartford, Conn, a corporation of Delaware Application March 27, 1945;. Serial No. 585,160

16. Claims.

This invention relates to free-piston units and particularly to an arrangement for circulating a cooling fluid through the piston assemblies.

Fluid has been circulated through the racks which form a part of the synchronizing linkages, since these racks are connected, to-a part of. the piston assemblies. Although this arrangement is satisfactory, in many cases the coolant may leak and affect the supply of lubricationv to the linkage. A feature of this invention is an arrangement for maintaining a circulation of coolant through the piston assembly independently of the synchronizing mechanism.

During the reciprocation of the piston assemblies, the inertia forces acting on the coolant Within the piston are such that coolant will normally flow into the piston during part of the piston stroke and. will tend: to discharge from the piston during the remainder of thestroke. To assure a flow of coolant, it may be necessary toprovide valves to prevent the inertia forces from causing an undesirable flow of'the coolant. A feature of this invention is an arrangement by which the valves are opened andclosed by the piston movement.

Another feature is an: incorporation of the valves as an integral part of the coolant circulating system.

Inusing telescoping tubes for delivering the coolant to or discharging it from the piston, the stationary tube is normally secured at one. end only in order to: permit the moving tube on' the pistonto reciprocate; The tubes may, during operation, become so out of line that they bind or do not function satisfactorily. A feature of this invention isthe use of athrough tube which may be. supported at. both ends and over which the piston reciprocates. Another feature is the arrangement of the tubes for controlling the flow of coolant into and out of the piston.

In using telescoping tubes for admitting fluid to the piston it has been customary to use the variable volume within the tubes to cause a pumping action by which the coolant is circulated through the piston. At high speed, the inertia forces acting on the coolant in the piston ma oppose. this pumping action to such an extent that undesirably high pressures. develop' in the coolant system. A feature of this. invention is an arrangement of the coolant tubes in such a manner: that they inertia forces are utilized to assist the coolantcircul'ation instead of'opposing it.

Other objects and advantages will be; apparent from. the specification andclaims and from ac stroke,

2. companying drawings which illustrate an embodiment of the invention. r

Fig. l is: a sectional view through the, freepiston unit. s

Fig. 2 is a sectional View through a piston: assembly.

Fig. 3' is a sectional View through, the coolant outlet device.

Fig. 4 is a fragmentary sectional View showing the arrangement of thevalve; in the. coolant inlet device.

Fig. 5 shows a. modified: form of coolant tube.

Fig. 6 is a sectional: view through. one end of the unit, substantially at right angles to: the section of Fig. 1. s

The unit. shown includes anengine cylinder Ill having reciprocating pistons l2 and l 4= to which compressor pistons I6 and I8 in; cylinders 20 and 22 are integrally connected. Sleeves 24 and 26 attached to the compressor pistons complete the reciprocating piston assembly, The sleeves in combination with stationary pistons. 28, and 30 formair-spring cylinders.

The pistons are moved apart by the burning of fuel injected into engine, cylinder I0 through one or more nozzles 32'. Air compressed in the air spring cylinders on the power stroke, returns the piston assembly. The pistons are always maintained at equal distances from the center of the engine cylinder-by alinkage which may include racks extending from the piston assemblies and meshing with a pinion, not shown.

Intake manifold 42-, which extends around the compressor and engine cylinders, conducts-air to intake valves 44 in the heads of the compressor cylinders, through which air automatically enters at opposite ends of: the cylinders. Compressed air leaves the cylinders through dischargevalves All, also: at opposite ends of the compressor cylintiers and passes into a center scavenge chamber ie and end; chambers Wand 5:2; Thesev chambers may be connected by a scavenge; manifold. not

shown.

Compressed gas from the. scavenge chambers enters engine ports 54 and 56 which are uncovered by pistons l 2 and I l at the endfofthespowei' thereby permitting.- air to be blown through the engine cylinder. G'as in the engine cylinders is discharged: through exhaustrportsili into exhaustmanifold 60;

The compressor cylinders may be: unloaded by the use, of rows of spill ports 63 in the cylinder walls. The effective volume of the compressor cylindersis determined'bythe number of rows of spill ports that are, closed. This: structure is and 86.

has a passage 62 in the compressor piston I8 which communicates with a tube 64 positioned centrally within the engine piston I4. Coolant passing through the tube 64 is discharged into a space 65 between the engine piston and a shield 66 positioned within the engine piston. This space is connected by passages I58 and a radial passage Ill with the fluid discharge.

During approximately the last half of the inward stroke of the piston assembly, the piston assembly is decelerating and the inertia forces on the coolant cause it to flow toward the head of the piston and thus permit flow of coolantinto the piston at a low pressure. Also, durin approximately the first half of the outward stroke,

As shown in Fig. 3, the coolant outlet device includes a tube I2 extending from a bracket I4 which may be integral with the wall I6, Fig. 1, of the center scavenge chamber 50. The other end of the tube is supported in a bracket I8 integral with the end cap' 89 that forms the scavenge chamber 52.

The ends of the tube are supported by packings 82 and 84 in the brackets I4 and I8 respectively. These packings allow a slight radial movement of the tube, and they may also permit expansion of the tube both radially and axially resulting from changes in temperature of the coolant.

Surrounding the tube I2 is another tube 85 supported centrally by the compressor piston I8, being locked in place by a clamping ring 88. This tube has passages 90 communicating with the passage III in the compressor piston. The ends of this tube 86 slide within seals 92 and 94 in the inner and outer heads 96 and 98 of the compressor cylinder and, as shown, tube 86 is short enough to permit reciprocation over the tube I2 without engaging the packings 82 and 84.

From a point adjacent to the center of the compressor cylinder 22 to'a point adjacent the outer cylinder head 98, the tube 12 is reduced in diameter to form a chamber I68 between tubes I2 Ports I02 permit flow of coolant into the tube from the chamber II!!! and communicate with the end of passage 90 during approximately the outer half of the stroke of the compressor piston.

I The inertia of the coolant within the piston is used to cause it to flow out of the piston. During approximately the last half of the outward stroke I outer (right hand, Fig. 2) end of the space 65 and to discharge through passages 68, I0 and 95 into the chamber I00, and thence into tube I2. From tube I2 coolant discharges through a conduit I04 connecting with a passage I06 in a cap I08 on the bracket I8,

During approximately the first half of the in ward piston stroke, the inertia forces act on the coolant to cause it to discharge from the piston along the same path. On the last half of the inward piston stroke and the first half of the outward stroke the accelerations are such that the coolant flows toward the head of the piston so no discharge of coolant will take place; during this Part of the stroke chamber IE0 is out of communication with ports 99 and the discharge passage is'thus closed.

The supply of fluid to the piston is controlled by may flow into the piston from tube I I0 only during the latter half of the inward stroke of the piston or the first half of the outward stroke,

the coolant also flows toward the pi'stonhead by reason of the inertia forces so that coolant may be admitted at a low pressure during this time. 7

It will thus be apparent that the piston coolant outlet is open during the part of the piston stroke when the inertia forces on the coolant will cause a discharge of the fluid from the piston, and the inlet is open when the inertia forces are reversed and will permit a flow of coolant into the piston.

The coolant tubes thus act as conduits through which coolant may flow into and out of the piston but do not, in themselves perform any pumping.

When coolant tubes of the conventional type are 7 used, the pumping action of the telescoping tubes must'take place in spite of the inertia forces on the coolant in the piston. The present arrangement of through tubes eliminates this pumpin action and permits the flow to occur as a result of the inertia forces on the coolant.

The space surrounding tube I2 at each end, that IOlllldS the tube I2 and is held in place by a clamping ring I26. Thissleeve together with a cylindrical opening I28 in head 89 collects any coolant escaping between the tubes. This space may be connected to a drain by a conduit I30.

Instead of a continuous through tube such as the tubes I2 and IIS it may be advantageous for the purpose of eliminating restrictions to the coolant flow, that the coolant be supplied through spaced tubes I32 and I34 as shown in'Fig. 5. The adjacent ends of the tubes are spaced apart an amount corresponding to the length of the reduced portion of the tube 12 and the tubesfit inside of a sleeve I36 corresponding to either of sleeves I00 or H2. separate tubes it may be advantageous to support the tubes against axial movement as, for example, by a, projecting flange I38 on the outer'end of tube I 34. This flange fits between the bracket I4!) corresponding to the bracket "I8 and a cap I42 mountedon the bracket. A sealing ring I44 may be used to prevent leakage around the end of the tube. The arrangement of ring I44 may.

be such that it will permit a slight lateral movement of the tube, the flange I38 being slightly,

smaller than the opening in the bracket to provide for such movement.

It is to be understood that the invention is not limited to the specific embodiment hereinillus trated and. described, but may be used in other ways without departure from its spirit as defined With this arrangement of j tion with said pistons and fitting over the coolant tubes.

2. In a free-piston unit'having a reciprocating piston, cylinders in which the piston reciprocates, coolant tubes extending from one of the cylinders in parallel relation to the piston reciprocation, and tubes mounted in the pistons for reciprocation with said pistons and fitting over the coolant tubes, said piston having a, passage communicating with the tubes mounted in the piston.

31 In a free-piston unit having a reciprocating piston, cylinders in which the piston reciprocates, coolant tubesextending from one of the cylinders in parallel relation to the piston reciprocation, and tubes mounted in the pistons for reciprocation with said pistons and fitting: over the coolant tubes, said piston having a passage communicating with the tubes mounted in the piston, and means for delivering coolant to one of said-coolant tubes.

4. In a free-piston unit having a reciprocating piston, cylinders in which the piston reciprocates, coolant tubes extending from one ofthe cylinders in parallel relation to the piston reciprocation, and tubes mounted in the pistons for reciprocation with said pistons and fitting over the coolant tubes, the coolant tubes being constructed to admit coolant from one of the tubesto the piston and to admit coolant from the piston into the other tube.

5. In a free-piston unit having a reciprocating engine piston, a cylinder in which the piston reciprocates, and a compressor cylinder and piston, the latter being connected to and moving with the engine piston, a cool-ant tube mounted at least at one end' in the compressor cylinder and extending through the compressor piston, and a tube mounted in the compressor piston and fitting over the coolant tube.

6; In a free-piston unit having a reciprocating engine piston, a cylinder in which the piston reciprocates, and a compressor cylinder and piston, the latter being connected to and moving with the engine piston, a coolant tube mounted at least at one end in the compressor cylinder and extending through the compressor piston, and a tube mounted in the compressor piston and fitting over the coolant tube, said piston having means for delivering coolant from the coolant tube to the engine piston.

7. In a free-piston unit having a reciprocating engine piston, a cylinder in which the piston reciprocates, and a compressor cylinder and piston, the latter being connected to and moving with the engine piston, a coolant tube mounted at least at one end in the compressor cylinder and extending through the compressor piston, and a tube mounted in the compressor piston and fitting over the coolant tube, said coolant tube being constructed to provide a connection from said tube to the surrounding tube mounted in the piston during a portion only of the piston reciprocation.

8. In a free-piston unit having a reciprocating engine piston, a cylinder in which the piston reciprocates, and a compressor cylinder and piston, the latter being connected to and moving with the engine piston, a coolant tube mounted at least at one end in the compressor cylinder and extending through the compressor piston, and a tube mounted in the compressor piston and fitting over the coolant tube, said coolant tube having a passage therethrough, andsaid piston having a cooperating passage through which coolant flows.

9; In afree-piston unit having a reciprocating engine piston, acylincler in Which the piston recipr'ocates, and a compressor cylinder and piston, the latter being connected to. and. moving with the engine piston, a coolant tube mounted at least atone end in the compressor cylinder and extending through the compressor piston, and a tube mounted in the compressor piston and fitting. over. the coolant tube, said coolant tube having a passage therethrough, and said piston having. a cooperating passage through which coolant flows, said passages being arranged to provide fora circulation of coolant during a portion only of the piston reciprocation.

10. In a free-piston unit having a reciprocating engine piston, a cylinder in which the piston reciprocates, and a compressor cylinder and piston, the latter being connected to and moving with the engine piston, a coolant tube mounted at least at one end in the compressor cylinder and extending through the compressor piston, and a tube mounted'in the compressor piston and fitting over'the coolant tube, said coolant tube having a reduced portion extendin approximately from the midpoint of thecompressor cylinder to a point adjacent one head of the cylinder, thereby providing for flow of coolant through the tube during a portion only of the piston reciprocation.

11. Ina free-piston unit, engine and compressor cylinders, a piston assembly including engine and compressor pistons fitting in the cylinders, said engine piston projecting from one side. of the compressor piston. and having a chamber therein. through which coolant may circulate, passagesin said compressor piston communicating with said chamber; and tubes extending through. the compressor piston and parallel to the direction of reciprocation of the piston. assembly, the passages, in the compressor piston communicatin with these tubes, in; combination with coolant: tubes mounted in the compressor cylinder and cooperating with the tubes in the piston to form an extensible duct through which coolant may be delivered to or discharged from the piston assembly.

12. In a free-piston unit, engine and compressor cylinders, a piston assembly including engine and compressor pistons fitting in the cylinders, said engine piston projecting from one side of the compressor piston and having a chamber therein through which coolant may circulate, passages in said compressor piston communicating with said chamber, and tubes extending through the compressor piston and parallel to the direction of reciprocation of the piston assembly, the passages in the compressor piston communicating with these tubes, in combination with coolant tubes mounted in the compressor cylinder and cooperating with the tubes in the piston to form an extensible duct through which coolant may be delivered to or discharged from the piston assembly, said coolant tubes extending through the tubes on the piston.

13. In a free-piston unit, engine and compressor cylinders, a piston assembly including engine and compressor pistons fitting in the cylinders, said engine piston projecting from one side of the compressor piston and having a chamber therein through which coolant may circulate, passages in said compressor piston communicating with said chamber, and tubes extending through the compressor piston and parallel to the direction of reciprocation of the piston assembly, the passages in the compressor piston communicating with these tubes, in combination with coolant tubes mounted in the compressor cylinder and cooperating with the tubes in the piston to form an extensible duct through which coolant may be delivered to or discharged from the piston assembly, said coolant tubes extending through the tubes on the piston, and being supported at least at one end in the compressor cylinder.

14. In a free-piston unit having a reciprocating engine piston, a cylinder in which the piston reciprocates, and a compressor cylinder and piston, the latter being connected to and moving withthe engine piston, coolant tubes mounted at least at one end in the compressor cylinder and extending through the compressor piston, and tubes mounted in the compressor piston-and fitting over the coolant tubes, said coolant tubes having a reduced portion extending approximately from the midpoint of the compressor cylinder to a point adjacent one head of the cylinder, thereby providing for flow of coolant through the tube during a portion only of the piston reciprocation, one of said coolant tubes being the inlet tube and being constructed to communicate with the inlet passage in the piston during approximately the inner half of the stroke of the piston.

15. In a free-piston unit having a reciprocating engine piston, a cylinder in which the piston reciprocates, and a compressor cylinder and piston,

the latter being connected to and moving with the engine piston, coolant tubes mounted at least at one end in the compressor cylinder and extending through the compressor piston, and tubes a mounted in the compressor piston and fitting over the coolant tubes, each of said coolant tubes hav-- ing a reduced portion extending approximately from the midpoint of the compressor'cylinder to a point adjacent one head of the cylinder, thereby providing for flow of coolant through the, tube during a portion only of the piston reciprocation,

one of said tubes being the inlet tube and being I constructed to communicate with the inlet passage in the piston during approximately the inner half of the stroke of the piston, and the other coolant tube being the outlet tube and being constructed to communicate with the outlet passage in the piston during approximately the outer ha of the stroke of the piston assembly.

16. In a free-piston unit, an engine cylinder,

a compressor cylinder, a piston assembly including engine and compressor pistons reciprocating in said cylinders, a' pair of stationary coolant tubes extending from oneof the cylinders in parallel relation to the direction of piston recipro-' cation, said tubes extending through openings in the compressor piston, and sleeves mounted over the coolant tubes and supported by the compressor pistons, an inlet andzan outlet passage in nEFnnnNons orrnn The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 673,029 Raymond Apr. 30, 1901 1,935,180 Edwards Nov. 14, 1933 2 289,153

Townsend July 7, 1942 

